Mishkat al-Masabih #443

Ibn ‘Umar said that when God’s messenger was asked about water in desert country and what is frequented by animals and wild beasts, he replied, “When there is enough water to fill two pitchers it bears no impurity.” Ahmad, Abu Dawud, Tirmidhi, Nasa'i, Darimi and Ibn Majah transmitted it. Another version by Abu Dawud has, “It does not become unclean.”